1. Field of the Invention
The present invention relates generally to a system for measuring a traveling direction or azimuth of a vehicle based on the geomagnetism around the vehicle and, more specifically, to a vehicular traveling direction measuring system which is capable of providing an accurate measurement of a traveling direction of the vehicle even when the environmental geomagnetism is disturbed.
2. Description of the Prior Art
When the vehicle is running on a bridge or on a high level road, geomagnetic disturbance components are increased in the output of the geomagnetic sensor installed on a vehicle body. The geomagnetic disturbance components are caused by magnetic metallic structural members, such as, steel frames and steel reinforcing rods, of the bridge or the high level road. Under such conditions, it is difficult to detect a traveling direction of the vehicle precisely with the conventional system of the type which derives the vehicular traveling direction based on the monitored geomagnetism around the vehicle.
In order to overcome the above-noted defects inherent in the conventional system, it has been proposed to average the output values of the geomagnetic sensor and to calculate the vehicular traveling direction based on the averaged sensor output data.
However, in order to obtain practically reliable averaged sensor output data which is substantially free from the affection of the magnetic disturbance components, an averaging time period for the sensor output data inevitably increases, leading to deterioration of the response characteristic of the system particularly when the vehicle turns a curve or a corner along the road.